Describing data is an important skill. Data visualization allows readers to get a concept of the data from a single display. To describe qualitative data we can break data down into categories called classes.
A class is one of the categories into which qualitative data can be classified. 
The class frequency is the number of observations in the data set that fall into a particular class. 
The class relative frequency is the class frequency divided by the total number of observations in the data set; that is,
\[class\,relatve\,frequency\,=\frac{class\,frequency}{n}\]

The class percentage is the class relative frequency multiplied by 100; that is,
\[class\,percentage\,= (class\,relative\,frequency) \times 100\]

With the above calculations you can display the data in a bar graph or pie chart.